1. Technical Field
The invention relates to a circuit arrangement for telecommunication switching systems, in particular to concentrator sub-exchanges connected to a central control exchange via the seizable connecting channels of two channel systems which are independent of each other, and in which a given number of said connecting channels belong to two transmission systems which, respectively, are provided with a common transmission medium per system and two common terminals per system, and in which one of the channels of each of the two transmission systems is used as a control signal, and in which subscriber line circuits connected to the sub-exchanges are cylically selected by each of two independently operating processors, said processors being provided in the concentrator sub-exchange in question and assigned to one of the two transmission systems, and are scanned for switching codes received via the subscriber line, for example, initial identification codes indicating the start of an intended connection which is to be established, as well as selection codes, special codes, release codes, etc., and in which the processors, in the event of a malfunction of their respective transmission systems, adopt an emergency operating mode which differs from the standard operating mode.
2. Description of the Prior Art
A circuit arrangement of this type is already known from the German application of F. Hilliges, No. 3,224,459 C2 published Jan. 5, 1984. It shows, among other things, that in the event of a malfunction occurring in the two channel systems, an emergency mode is maintained in the concentrator sub-exchange by continuing to establish connections between the subscriber line circuits which are connected to the same concentrator. Therefore, the so-called island exchange operation is continued while only internal traffic is handled. In addition, it describes the operating mode of the two concentrator processors in the event that the channel system of one of the two processors is faulty, but that of the other is not. In this case, it is stated that one of the two processors handles only internal traffic (in accordance with the above "island exchange operation") and the other external traffic, i.e., via the channel system of this processor, which is still operative. As it is not clear when the circuit is initially seized (that is, every time a subscriber wishes to establish a call in the process of which the subscriber loop closes via its subscriber station) whether an internal or external connection is to be established, the known circuit arrangement specified in the above document provides that a data exchange take place between the two concentrators, so that a connection can always be established by the processor responsible during such an operating mode.
If the operation is to be highly un-susceptible to malfunction, it is practical for the processors to be so designed that they operate, as much as possible, independently of each other, so that a malfunction occurring in one of the two processors will not affect the other processor. It is thus advantageous to decouple the two processors from each other completely, so that they are able to function with total independence from each other. Moreover, the existence of two completely independent channel systems ensures that an adequate emergency mode can be adopted in the event that one of the two channel systems breaks down, while the other is still operative. In this connection, it is rather important that a processor whose channel system malfunctions may only handle island exchange traffic when it is no longer possible to establish connections via the higher ranking exchange. As, however, a reciprocal information exchange between the two processors is not to take place for the aforementioned reasons, in the case of a processor whose channel system malfunctions while the processor itself still is in working order, the problem arises of obtaining orientation assistance whereby the processor is either forced to perform or prohibited from performing island exchange operations.
It is the objective of the present invention that in a circuit arrangement of the type described above, the handling of the emergency operating state (island exchange operation) be accomplished without direct interaction of the two processors.